Description: SAMpower computes the Hilbert envelope of power for continuous data and outputs a 3D+time image. It does not compute event-related power (for which see, SAM3d/SAM3dc, SAM4d/SAM4dc, or SAMersc). SAMpower is intended for use in connectivity studies of the correlation of the envelope of power among voxels -- e.g., by using ICA or the AFNI, function "Instacorr".

SAMpower applies the beamformer coefficients to the filtered MEG data (specified by ImageBand) to compute the estimated source time-series. It then applies the Hibert transform to obtain the envelope of power. This is followed by a lowpass filter (specified by SmoothBand) and resampling at the interval specified by TimeStep. The smoothed resampled Hilbert envelope of power is written out to each voxel.

Usage:

SAMpower -r <dataset_name> -m <parameter_file_name> -v

The -r flag is followed by the dataset name (with or without the .ds suffix). The -m flag is followed by the parameter file name without the .param suffix. The -v argument specifies verbose output — else SAMpower works silently.

The required parameter file keywords for SAMpower are:

• RemoveBaseline — designates which option is used for baseline removal. The choices are NONE, BYVOXEL, or GLOBAL.
• CovBand — designates designates the subdirectory from which the beamformer coefficients (weights) are read
• ImageBand — designates the bandpass for image the power
• SmoothBand — designates the lowpass filter for smoothing the Hilbert envelope
• ImageMetric — selects images as a function power
• NumMarkers — must be 0 (zero)
• CovType — must be GLOBAL

Optional keywords include:

• ImageFormat — designates whether the ortho or Talairach beamformer weights are selected
• ImageDirectory — designates the directory where the NIFTI image files are written (default is the SAM subdirectory)
• PrefixLength — designates the number of leading characters in the MEG dataset name are extracted for naming files. The default is the 8-character hash-code used for NIMH MEG datasets. The prefix is also used to select the MRI subdirectory (as used by SAMwts)

Examples parameters for imaging the Hilbert envelope of beta-band power in Taliarach space on an 8mm grid:

NumMarkers	0
CovBand	4.0	50.0
ImageBand	14.0	30.0
SmoothBand	0.0	5.0
XBounds	-12	12
YBounds	-9	9
ZBounds	-2	15
ImageStep	0.5
ImageFormat	TLRC	8.0
Mask	/data2/Mask8mm.nii
ImageMetric	Power
CovType	GLOBAL
MRIDirectory	/data1/mri
ImageDirectory	/data1/Rest/Images
TimeStep	0.1
RemoveBaseline	BYVOXEL